Motor operated tap changer employing contact drum switches

ABSTRACT

Tap position selector device for controlling a motor operated tap changing mechanism. A selector switch is connected to two multiple contact drum switches. The drum switches are interconnected so that one drum switch conducts only when the selector switch requires that the tap position be raised and the other drum switch conducts only when the selector switch requires that the tap position be lowered. The movable contacts of both drum switches move with the tap changing mechanism.

United States Patent Prescott [4 1 May 16, 1972 [541 MOTOR OPERATED TAP CHANGER [56] References Cited EMPLOYING CONTACT DRUM UNITED STATES PATENTS SWITCHES 2,774,934 12/1956 Gitzendanner ..323/43.5 R [72] Inventor; Herbert L Prescott, B kfidd Ohio 3,423,657 1/1969 Ponstingl et al ..323/43.5 R X [73] Assignee: Westinghouse Electric Corporation, Pitt- P i E i Ge 1d G ldb r sburgh, Pa. Att0rney-A. T. Stratton and F. E. Browder PP 4 141,147 Tap position selector device for controlling a motor operated tap changing mechanism. A selector switch is connected to two multiple contact drum switches. The drum switches are [52] US. Cl. 323/43.5 R interconnected so that one drum Switch Conducts only when I 5 l I llll. Cl. 1/14 th l t wit h requires that the tap position be raised and [58] Fiel of elr h l the other drum switch conducts only when the selector switch Lil LOWER ING requires that the tap position be lowered. The movable contacts of both drum switches move with the tap changing mechanism.

4 Claims, 1 Drawing Figure Patented May 16, 1972 4 0053mm OZEUEOJ JOmEZOO w BACKGROUND OF THE INVENTION 1 Field of the Invention This invention relates, in general, to electrical inductive apparatus and, more particularly, to control circuitry for motor activated tap changers.

2. Description of the Prior Art Changing taps on a tapped winding is usually accomplished with the aid of a set of fixed and movable contacts. The fixed contacts are connected to the tap leads of the tapped winding and the movable contacts are connected to the source or load which is being electrically connected to the tapped winding. In high power applications, especially in underload tap changers,

' the movable contacts are frequently moved by a mechanical means which is driven by an electric motor. The motor is operated. manually by a tap position selector switch or automatically by means of computer or error detector devices.

The associated control circuitry required to energize the tap changing motor and deenergize it when the correct position is reached, according to the prior art, is relatively complex. The complexity of the position selector control circuitry increases as the number of tap positions increases. According to the prior art methods, a separate drum switch is required for each tap position. As the number of tap positions desired is increased to achieve greater regulation or input control, the economic feasibility and reliability of the control circuitry is substantially degraded. Therefore, it is desirable to provide a tap position selector device which readily permits multiple tap position selection without the need for an excessive number of drum switches.

It has also been characteristic of prior art tap control circuitry to require a complicated switching network to activate the control circuitry. It is desirable to provide a control circuit which can be activated by a single set of contacts for each tap position desired.

Certain tap changing applications require that only a portion of the taps be used during a particular period of time or during a certain type of operation. Welding applications frequently use different heat ranges for difierent work pieces. Thus, it is desirable to provide a control circuit which can readily select all the taps required during a particular operation or application while being versatile enough to select other tap positions for different operations with a minimum amount of circuit changes.

SUMMARY OF THE INVENTION This invention provides a new and improved position selector switching device for use with tap changing mechanisms. Only two drum switches are required regardless of the number of tap positions available. A selector switch, having a separate set of contacts for each tap position desired, is connected through a jack panel to the two drum switches. The jack panel is used to select the winding tap positions which will correspond to the desired position of the selector switch.

When a set of contacts on the selector switch are closed, a current flows through these contacts, through one of the drum switches and through a motor relay. If the selector switch contacts correspond to a higher tap position, the drum switch which is connected to the tap raising relay conducts. If the selector switch contacts correspond to a lower tap position, the drum switch which is connected to the tap lowering relay conducts. The movable contact assembly of the drum switches are mechanically connected to the tap changing contact drive mechanism. The motor will continue to run until the movable contact obtains a position where the switch does not conduct. The tap changer retains this position until the selector switch is changed.

BRIEF DESCRIPTION OF THE DRAWING Further advantages and uses of this invention will become more apparent when considered in view of the following 2' detailed description and drawing, in which there is shown schematically a position selector circuit constructed according to this invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Throughout the following description similar reference characters refer to similar elements in all parts of the drawing.

Referring now to the drawing, there is shown tap changing apparatus constructed according to this invention. A transformer 10 which is associated with the tap changing apparatus includes a tapped winding 12, a magnetic core 14 and a winding 16. A movable tap contact assembly 18 electrically connects a tap terminal 20 to the terminal 22. The terminals 22 and 24 and the terminals 26 and 28 may be connected either to a load circuit or to a power source. That is, the tapped winding 12 may be used to supply energy to the transfonner 10 or supply energy from the transformer 10 to an external load.

The basic arrangement shown for discussion in the drawing would be used in no load tapping service. However, this invention is also applicable to load tap changers. The movable tap contact assembly 18 in load service may be attached to or synchronized with other movable contacts to prevent interrupting the winding current while changing taps.

The movable tap contact assembly 18 may be a rotating arm having an arc of rotation such that the contacts 20 may be placed along the arc. The movable tap contact assembly 18 and the tap terminals 20 may also be aligned in linear relationship. The movable tap contact assembly 18 is attached by a drive mechanism 30 to a motor 32. The drive mechanism may include a combination of gears to change the speed of the motor 32 to the desired speed for moving the movable tap contact assembly 18. The motor 32 is powered by a motor power source 34 and controlled by a lowering relay contact 36 and a raising relay contact 38. When the lowering relay contact 36 is closed and the raising relay contact 38 is opened, the motor 32 operates in a direction which lowers the movable tap contact assembly 18, thus effectively decreasing the turns of the winding 12. When the raising relay contact 38 is closed and the lowering relay contact 36 is opened, the motor 32 operates in a direction which raises the movable tap contact assembly 18, thus efiectively increasing the turns of the winding 12. Arrows 40 and 42 respectively indicate the raising and lowering directions of the movable tap contact assembly 18.

The multiple contact rotary drum switches 44 and 46 respectively include rotary or movable drum contacts 48 and 50 and fixed drum contacts 52 and 54. The number of fixed drum contacts for each switch is dependent upon the number of tap positions desired for selection. As illustrated, each drum switch, 44 and 46, includes 17 fixed drum contacts 52 and 54, respectively, although this invention applies to drum switches having different numbers of fixed drum contacts. The drum switches 44 and 46 are arranged so that the fixed drum contacts 52 and 54, respectively, are capable of contacting the movable drum contacts 48 and 50, respectively. The movable drum contacts 48 and 50 are capable of contacting any number of the fixed drum contacts 52 and 54, respectively, which are adjacent. That is, the movable drum contact may contact any one fixed drum contact or any number of adjacent fixed drum contacts up to the maximum number of fixed drum contacts on the switch.

The movable drum contacts 48 and 50 are connected with the drive mechanism 30 so that when the movable contact assembly 18 moves, the movable drum contacts 48 and 50 move also. The direction of movement of the movable drum contacts 48 and 50 is indicated by the arrows 56 and 58, respectively. The movable drum contacts 48 and 50 move the same number of positions as the movable contact assembly 18. For example, when the movable contact assembly 18 changes three tap positions, the movable drum contacts 48 and 50 change three positions of the fixed drum contacts 52 and 54, respectively.

The fixed drum contacts 52 and 54 are interconnected as shown in the drawing. The movable drum contacts 48 and 50 are always positioned so that one pair of fixed drum contacts is not in contact with either of the movable drum contacts 48 and 50. The fixed drum contacts 60 and 62 are shown with this relationship in the drawing. The movable drum contact 48 is electrically connected to a raising motor relay coil 64, and the movable drum contact 50 is electrically connected to a lowering motor relay coil 66. The coils 64 and 66 are connected, as shown, to a control power source 68. The control power source may be of any type which is sufficient to activate the relay coils 64 and 66.

A selector switch 70 and a jack panel 72 are connected as shown in the drawing. The jack panel 72 comprises jacks 74 and plugs 76. The jacks 74 and the plugs 76 may be of any type which can be easily interchanged and are capable of safely handling the power level involved. The jack panel 72 may or may not be mounted physically close to the drum switches 44 and 46. The purpose of the jack panel 72 is to allow convenient circuit changes of the selector control circuit to make it versatile and compatible with a wide range of tapping requirements. For example, one operation of the tap changer may require that the leads coming from the selector switch 70 be plugged into the jack panel 72 as shown in the drawing to obtain a specified relationship between the selector switch 70 position and the winding tap position. Another operation may require a different relationship, thus the plugs may be readily rearranged to provide the desired relationship. This situation exists in many types of high power industrial resistance welding applications. A particular piece being welded may require several different current settings while another piece may require other settings. The jack panel affords a relatively simple means for setting up the control circuit to furnish the desired taps. v

The selector switch 70 may or may not be positioned physically near the drum switches 44 and 46 or the tapped transformer 10. The selector switch 70 is represented in the drawing by the eight sets of contacts, however, any number equal to or less than the number of tap positions available may be used. The contacts may be interlocked so that only one set can be closed simultaneously. The contacts may be connected to, or replaced by, computer or error detector outputs so that the tapping operation may be controlled automatically.

The drawing represents the state of the circuit after a tap change has been made. That is, the motor 32 is not running. If it is desired to change the tap position, a contact of the selector switch 70 corresponding to the tap position desired is closed. For example, when the contact 78 is opened and the contact 80 is closed, a current path exists through the jack panel 72, the fixed drum contact 82, the movable drum contact 50 and the lowering relay coil 66. This closes the contacts 36 and energizes the motor 32, thus the movable contact assembly 18 moves in a lowering direction. The movable drum contact 50 rotates in a clockwise direction and the movable drum contact 48 rotates in a counterclockwise direction. This rotation continues until the movable drum contact 50 does not contact the fixed drum contact 82, at which time the current path is interrupted and the motor 32 is stopped. The tap changer retains this position until the selector switch 70 is changed by closing another set of contacts. The tap raising procedure is similar except that the direction of movement of the movable contacts is reversed.

I claim as my invention:

l. A position selector control device for tap changing apparatus comprising first and second rotary drum switches each having a rotary contact assembly and a plurality of fixed contacts, said rotary contact assemblies being connected to a motor which moves the tapping contacts so that one said rotary contact assembly rotates in a direction which increases the number of fixed contacts it touches while the other said rotary contact assembly rotates in a direction which decreases the number of fixed contacts it touches, and said fixed contacts of said first rotary drum switch being electrically connected to said fixed contacts of said second rotary drum switch at respective positions to form a plurality of fixed contact pairs, said rotary contact assemblies always being relatively positioned so that only one of said fixed contact pairs is not touched by either of said rotary contact assemblies.

2. The position selector control device for tap changing apparatus of claim 1 including a selector switch having a plurality of contact sets each being electrically connected to said fixed contact pairs of said rotary drum switches through patch panel means, said patch panel means allowing a quick change of the electrical connection of said selector switch contact sets from one of said fixed contact pairs to another of said fixed contact pairs.

3. A position selector control device for tap changing apparatus comprising a selector switch, first and second rotary drum switches, first and second motor relays, said selector switch having a plurality of contact sets which are electrically connected to said rotary drum switches, said first and second motor relays being electrically connected to said first and second rotary drum switches, means energizing said first motor relay to cause a motor to move the tapping contacts in one direction and means energizing said second motor relay to cause said motor to move the tapping contacts in the opposite direction, said rotary drum switches each having a rotary contact assembly which is connected to said motor so that closing a set of contacts of said selector switch causes one of said motor relays to energize until one of said rotary contact assemblies rotates to a position which deenergizes said motor relay.

4. Tap changing apparatus comprising a transformer having a tapped winding, a movable tapping contact for connecting an external circuit to said tapped winding, drive means including a motor for moving said tapping contacts, a selector switch having a plurality of contact sets, first and second rotary drum switches each having a rotary contact assembly and a plurality of fixed contacts, said rotary contact assemblies being connected to said motor so that when said motor is operating one said rotary contact assembly rotates in a direction which increases the number of fixed contacts it touches while the other said rotary contact assembly rotates in a direction which decreases the number'of fixed contacts it touches, said fixed contacts of said first rotary drum switch being electrically connected to said fixed contacts of said second rotary drum switch at respective positions to form a plurality of fixed contact pairs, said rotary contact assemblies always being relatively positioned so that only one of said fixed contact pairs is not touched by either of said rotary contact assemblies, said contact sets of said selector switch each being electrically connected to said fixed contact pairs of said rotary drum switches through patch panel means, said patch panel means allowing a quick change of the electrical connection of said selector switch contact sets from one of said fixed contact pairs to another of said fixed contact pairs. 

1. A position selector control device for tap changing apparatus comprising first and second rotary drum switches each having a rotary contact assembly and a plurality of fixed contacts, said rotary contact assemblies being connected to a motor which moves the tapping contacts so that one said rotary contact assembly rotates in a direction which increases the number of fixed contacts it touches while the other said rotary contact assembly rotates in a direction which decreases the number of fixed contacts it touches, and said fixed contacts of said first rotary drum switch being electrically connected to said fixed contacts of said second rotary drum switch at respective positions to form a plurality of fixed contact pairs, said rotary contact assemblies always being relatively positioned so that only one of said fixed contact pairs is not touched by either of said rotary contact assemblies.
 2. The position selector control device for tap changing apparatus of claim 1 including a selector switch having a plurality of contact sets each being electrically connected to said fixed contact pairs of said rotary drum switches through patch panel means, said patch panel means allowing a quick change of the electrical connection of said selector switch contact sets from one of said fixed contact pairs to another of said fixed contact pairs.
 3. A position selector control device for tap changing apparatus comprising a selector switch, first and second rotary drum switches, first and second motor relays, said selector switch having a plurality of contact sets which are electrically connected to said rotary drum switches, said first and second motor relays being electrically connected to said first and second rotary drum switches, means energizing said first motor relay to cause a motor to move the tapping contacts in one direction and means energizing said second motor relay to cause said motor to move the tapping contacts in the opposite direction, said rotary drum switches each having a rotary contact assembly which is connected to said motor so that closing a set of contacts of said selector switch causes one of said motor relays to energize until one of said rotary contact assemblies rotates to a position which deenergizes said motor relay.
 4. Tap changing apparatus comprising a transformer having a tapped winding, a movable tapping contact for connecting an external circuit to said tapped winding, drive means including a motor for moving said tapping contacts, a selector switch having a plurality of contact sets, first and second rotary drum switches each having a rotary contact assembly and a plurality of fixed contacts, said rotary contact assemblies being connected to said motor so that when said motor is operating one said rotary contact assembly rotates in a direction which increases the number of fixed contacts it touches while the other said rotary contact assembly rotates in a direction which decreases the number of fixed contacts it touches, said fixed contacts of said first rotary drum switch being electrically connected to said fixed contacts of said second rotary drum switch at respective positions to form a plurality of fixed contact pairs, said rotary contact assemblies always being relatively positioned so that only one of said fixed contact pairs is not touched by either of said rotary contact assemblies, said contact sets of said selector switch each being electricallY connected to said fixed contact pairs of said rotary drum switches through patch panel means, said patch panel means allowing a quick change of the electrical connection of said selector switch contact sets from one of said fixed contact pairs to another of said fixed contact pairs. 